The invention relates to a radiant heater. The invention specifically relates to a radiant heater for placing beneath a cooking area, particularly a tempered glass or glass ceramic plate, having a carrier shell, which carries an insulator, on and/or in which is located a heater forming a heating zone, and with at least one elongated temperature sensor of a protective switch projecting over part of the heating zone and running between the latter and the cooking area, the sensor being retained by the insulator and fastening means reaching the carrier shell.
Such radiant heaters conventionally have a temperature sensor, whose outer tube is made from an insulating material, particularly quartz or quartz glass. It is either incorporated into the expansion system of the sensor, in which it forms a tube with a low expansion coefficient, in which is located a tension bar with a higher expansion coefficient, or it is shoved onto an expansion tube. This is necessary in order to ensure the necessary air gaps or leakage distances in the space between the heating resistors and the plate through which the temperature sensor passes. It must be borne in mind that glass ceramic plates become electrically conductive at the operating temperature, so that here the necessary insulation distances must be maintained.
A sensor fastening of this type is described by DE 35 36 981. As sensor fastenings are proposed spacers with respect to the glass ceramic plate and the insulator. The sensor can also be fastened in the insulator by nail clamps or the like.
DE 91 13 992 describes a sensor fastening, in which the retaining clips embrace the sensor and are guided by the insulator and carrier shell and behind the passage through said shell have a locking member preventing an extraction from the carrier shell. Inter alia such a sensor fastening ensures that the sensor does not strike against the glass ceramic plate, which could lead to the breakage of the latter. This can occur both during testing and during the transportation or installation of a cooking area.
The problem of the invention is to provide a radiant heater of the aforementioned type in which a reliable sensor fastening is possible, whilst also bringing about an improvement to the fitting of both the sensor fastening and the radiant heater, together with the subsequent working of the finished radiant heater.
This problem is solved independently by the features of claim 1, claim 11, claim 21 and claim 31. Advantageous developments of the invention form the subject matter of the dependent claims and are described hereinafter. The essence of the invention is that the fastening means are at least partly shaped from the material of the carrier shell. On fastening temperatures sensors to radiant heaters using conventional fastening means generally openings or holes are e.g. punched out on the carrier shell and in them are then inserted and secured the fastening means. However, waste occurs with this process and said waste material can stick to the punching tool and make it dirty. As a result exact, clean punching is no longer possible. The punching tool must be cleaned or, if necessary, replaced which takes up a relatively large amount of time. The punched out openings or holes are provided with projecting lugs or nozzles which prevent an exact fixing of the fastening means. These disadvantages are obviated according to the invention in that the fastening means are essentially formed from the same material as the carrier shell. Thus, there is no waste and there are no prejudicial openings or lugs.
Sheet metal is preferably used as the carrier shell material. Sheet metal is heat resistant and has a relatively low weight. In spite of this its carrying capacity is so high that it is able to carry the insulator. It would also be possible to use other heat resistant materials, such as ceramics or the like.
The fastening means preferably comprise a holder for holding the sensor and an abutment for securing the holder. Compared with the holder portion extending through the insulator, the abutment advantageously has a different configuration. Thus, it is possible for the abutment to be inclined or to be substantially transversely directed. Thus, e.g. a holding leg of the holder can be bent at right angles behind the insulator in order to prevent extraction. The holder is preferably retained by engaging the abutment with its entire or a large surface against the underside of the insulator. This reduces or eliminates the risk of the fastening being torn out of the insulator.
In particularly preferred manner the abutment is shaped out of the carrier shell. The abutment can be formed from several lugs formed out of the carrier shell and to which the holder can be fixed. However, preferably the abutment is shaped in one piece from the carrier shell, e.g. by a punching process, where two mirror symmetrical notches are punched into the carrier shell and the material between the two notches can then be bent up as abutments.
Preferably a locking connection is located between the holder and the abutment. It can have an insertion bevel for inserting the holder and a locking edge for locking a barblike end of the holder. On sliding over the insertion bevel the holder, e.g. two holding legs, can be elastically bent upwards to a certain extent. On reaching the locking edge, its barb-like end can engage below the locking edge and snap in. The abutment can have all conceivable cross-sectional shapes, e.g. an inverted V-shaped cross-section or a trapezoidal cross-section. However, it preferably has a substantially cap-shaped cross-section and a central portion of the abutment is arcuately directed towards the insulator and two lug-like legs of the abutment are bent away from the insulator. The arcuately constructed central portion can be supported on the underside of the insulator without damaging the latter, as could be the case with e.g. tapering central portions. To obtain a relatively large contact surface on the underside of the insulator, the central portion is preferably made wider than the two legs.
It is possible for the abutment to be formed in a bulge of the carrier shell directed towards the insulator, the carrier shell bulge projecting into an insulator bulge constructed in complimentary manner thereto. The two complimentary bulges on the carrier shell and insulator enable them to be stacked in one another.
The holder can have an elongated portion or long holding legs, which extend through the insulator up to the abutment. The holder or holding legs can preferably engage over or round in an at least partial manner said sensor and in this way position it, e.g. by pressing against the insulator.
The holder can be a clip with two legs and a U or O-shaped upper part for retaining the sensor. The upper part can extend or engage over the sensor and hold it in position, particularly by pressing against the insulator.
In an alternative the holder can be connected in one piece with the carrier shell and in this case the carrier shell forms the abutment. The carrier shell then engages on the underside of the insulator. Starting from the insulator, the holder can extend from the carrier shell to the sensor, which can e.g. project through a recess or receptacle in the vicinity of the upper portion of the holder.
One possibility for connecting the holder to a metal carrier shell is the welding or riveting of corresponding components. Preferably the holder is joined to or worked out from the carrier shell in one piece. This makes it possible to rough-work an elongated sheet metal strip separated by three notches, which form a U, from the carrier shell and bend or set up the same. The insulator can be engaged over the holder or at least one leg thereof. In particular during the fitting of the radiant heater, the holder can automatically pierce the insulator, at least partly project over the same and receive the sensor. Either the holder can pass through the insulator on engaging the latter or can project through a prefabricated slot in the insulator.
The invention also covers a radiant heater according to the preamble of claim 1, in which part of the fastening means is anchored in an abutment which is at least separate from the insulator, the abutment being located behind the underside of the insulator remote from the heater without projecting over the underside of the carrier shell remote from the insulator.
This makes it possible with radiant heaters having planar carrier shells to easily and advantageously stack the same, because the underside or the carrier shell is not projected over by interfering abutments or the like. In certain circumstances it is advantageously possible to economize the costs involved in providing the carrier shell from below with a recess for receiving the abutment.
Preferably the abutment is constructed separately from the carrier shell and can be anchored between the insulator and said shell.
One possibility for manufacturing the abutment involves the use of a firm, insulating material, e.g. vermiculite or the like. In it can be engaged at least one leg of the fastening means. A counterabutment is advantageously shaped like a disk and in particular with a large contact surface against the underside of the insulator. Further possibilities are truncated cones or cylinders.
These and further features can be gathered from the claims, description and drawings and the individual features, both individually and in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual segments and the subheadings in no way restrict the general validity of the statements made thereunder.